Presently available inductive proximity sensors require a high operating power which restricts their use in battery powered applications. The present invention uses reduced operating power by only applying power from a DC voltage supply to the inductor for a short time period needed to detect the presence or absence of an appropriate object. After the detection time period is over, DC voltage supply power is no longer applied to the inductor. As long as DC voltage supply power is applied to the inductor the current level increases. In the case of a capacitor the current level decreases with time. By waiting a relatively long time period between reapplication of DC voltage supply power to the inductor the power duty cycle is low causing the average power to be low. In addition by using CMOS logic circuitry which uses substantially no power, except during circuit signal level transitions, total sensor power is further reduced.
In addition the effects of temperature, supply voltage, and manufacturing tolerance can be reduced by using matched components and also ratios instead of absolute electrical values in the critical circuit sections. Most components especially those that are part of an Integrated Circuit can be readily built with a high level of electrical parameter matching while their absolute values have wide variations.
An objective of the present invention is to provide an inductive proximity sensor that operates at a low power level.
It is an additional object of the invention to provide an inductive proximity sensor that uses circuits that are less susceptible to process variances by relying on matched components and also ratios instead of absolute electrical values thereby providing a more consistently manufacturable circuit.
An additional object of the invention is to provide an inductive proximity sensor that uses circuits that have fast response time allowing a quick response to objects being sensed.
It is a further object of the invention to provide an inductive proximity sensor that uses circuits that are less susceptible to temperature and supply voltage variances by relying on matched components and also ratios instead of absolute electrical values.